The present invention is directed to the field of chemical vapor deposition of silicon dioxide and silicon oxynitride films using bis(tertiarybutylamino)silane, a novel organosilicon source material. It allows for the deposition of different dielectrics using the same organosilicon source, temperature, and pressure simply by varying reactant gases.
In the fabrication of semiconductor devices, a thin passive layer of a chemically inert dielectric material such as, silicon dioxide, silicon oxynitride and silicon nitride films, is essential. Thin layers of these dielectric films function as diffusion masks, oxidation barriers, trench isolation, intermetallic dielectric material with high dielectric breakdown voltages and as passivation layers.
The present semiconductor industry standard for silicon dioxide and silicon oxynitride growth methods is by low pressure chemical vapor deposition in a hot wall reactor at &gt;400.degree. C.
Deposition of silicon dioxide over large numbers of silicon wafers has been accomplished using silane and oxygen above 400.degree. C., by dichlorosilane and N.sub.2 O above 800.degree. C., and by tetraethoxysilane above 650.degree. C. Deposition of silicon oxynitride has been obtained using dichlorosilane, N.sub.2 O, and NH.sub.3 above 750.degree. C., see Semiconductor and Process technology handbook, edited by Gary E. McGuire, Noyes Publication, New Jersey, (1988), pp 289-301; and Silicon Processing for the VLSI ERA, Wolf, Stanley, and Talbert, Richard N., Lattice Press, Sunset Beach, Calif. (1990), pp 20-22, 327-330.
Higher deposition temperatures are typically employed to get the best film properties. There are several drawbacks in these processes, and some of these are as follows:
i) Silane and dichlorosilane are pyrophoric, toxic compressed gases; ii) Oxide depositions with dichlorosilane require very high temperatures and have very low deposition rates. The films may contain chlorine and there is a significant particle contamination problem. iii) Films formed using silane are not dense and are hygroscopic. This process requires expensive "caged boats" to obtain usable deposited film uniformities. Small deviations in oxygen to silane ratios may produce homogeneous reactions that will produce significant particle contamination.
A. K. Hochberg and D. L. O'Meara, Mat. Res. Soc. Symp. Proc,. Vol. 204, (1991), pp 509-514, report deposition of silicon nitride and silicon oxynitride by using diethylsilane with ammonia and nitric oxide by LPCVD. The deposition was carried out in the temperature range of 650.degree. C. to 700.degree. C. Usable deposition rates are obtained at temperatures above 650.degree. C. and the deposition rate drops to below 4 .ANG./min at lower temperatures. In the LPCVD process, precursors which contain direct Si--C carbon bonds result in carbon contamination in the films. Carbon free deposition requires greater than 5:1 NH.sub.3 to precursor ratios. At lower ammonia concentrations, the films were found to contain carbon. Diethylsilane+ammonia processes typically require covered boats to improve wafer uniformities.
Japanese Patent 6-132284 describes deposition of silicon nitride using organosilanes with a general formula (R.sub.1 R.sub.2 N).sub.n SiH.sub.4-n (where R.sub.1 and R.sub.2 range from H--, CH.sub.3 --, C.sub.2 H.sub.5 -- C.sub.3 H.sub.7 --, C.sub.4 H.sub.9 --) by a plasma enhanced chemical vapor deposition and thermal chemical vapor deposition in the presence of ammonia or nitrogen. The precursors described here are tertiary amines and do not contain NH bonding as in the case of the present invention. The deposition experiments were carried out in a single wafer reactor at 400.degree. C. at high pressures of 80-100 Torr. The Si:N ratios in these films were 0.9 (Si:N ratios in Si.sub.3 N.sub.4 films is 0.75) with hydrogen content in the deposited films. The butyl radical is in the form of isobutyl.
U.S. patent application Ser. No. 08/942,996 filed Oct. 2, 1997 discloses a process for the low pressure chemical vapor deposition of silicon nitride on a substrate using ammonia and a silane of the formula: (t-C.sub.4 H.sub.9 NH).sub.2 SiH.sub.2.
U.S. Pat. No. 5,234,869 and R. G. Gordon and D. M. Hoffman, Chem. Mater., Vol. 2, (1990), pp 482-484 disclose other attempts to reduce the amount of carbon involved aminosilanes, such as tetrakis(dimethylamino)silane. The temperature of deposition is in the range of 300-1000.degree. C. with pressures in the range of 1 mTorr-10 Torr. The presence of direct Si--N bonds and the absence of Si--C bonds were expected to give lower carbon concentrations in the films. Howeve, there are three main disadvantages with precursors of this class.
1) They contain N-methyl groups, the methyl groups tend to migrate to the silicon surface readily and contaminate the films with carbon during a CVD process. In order to reduce the amount of carbon, the process involves high temperatures (&gt;700) and high ammonia ratios (&gt;10:1). With increased ammonia ratios the deposition rates dramatically reduce due to reactant depletion. PA1 2) They do not contain NH bonding and they do not involve secondary silanes. PA1 3) At lower temperatures the deposition rates and uniformities are very poor (&gt;5%). PA1 a) heating a substrate to a temperature in the range of approximately 500-800.degree. C. in the zone; PA1 b) maintaining the substrate at a pressure in the range of approximately 20 mTorr-1 atmosphere in the zone; PA1 c) introducing into the zone a reactant gas of O.sub.2 and a silane of the formula: (t-C.sub.4 H.sub.9 NH).sub.2 SiH.sub.2 and reacting the reactant gas with the silane; and PA1 d) maintaining the conditions of a) through c) sufficient to cause a film of silicon dioxide to deposit on the substrate. PA1 a) heating a substrate to a temperature in the range of approximately 500-800.degree. C. in the zone; PA1 b) maintaining the substrate at a pressure in the range of approximately 20 mTorr-1 atmosphere in the zone; PA1 c) introducing into the zone reactant gases selected from the group consisting of N.sub.2 O, NO, NO.sub.2, and mixtures thereof, ammonia and a silane of the formula: (t-C.sub.4 H.sub.9 NH).sub.2 SiH.sub.2 and reacting the reactant gases with the silane; and PA1 d) maintaining the conditions of a) through c) sufficient to cause a film of silicon oxynitride to deposit on the substrate. PA1 a) heating the substrate to a temperature in the range of approximately 500-800.degree. C. in the zone; PA1 b) maintaining the substrate at a pressure in the range of approximately 20 mTorr-1 atmosphere in the zone; PA1 c) introducing into the zone a silane of the formula: (t-C.sub.4 H.sub.9 NH).sub.2 SiH.sub.2 ; PA1 d) introducing into the zone varying amounts of a reactant gas selected from the group consisting of O.sub.2, O.sub.3, N.sub.2 O, NO, NO.sub.2, NH.sub.3 and mixtures thereof appropriate to deposit multiple stacked layers of a film of a silicon compound containing silicon and one or more of oxygen, nitrogen and mixtures thereof, wherein each stacked layer can have a different amount of oxygen, nitrogen and mixtures thereof and reacting the reactant gas with the silane; PA1 e) maintaining the conditions of a) through c) sufficient to cause the multiple stacked layers of a film of the silicon compound to deposit on the substrate.
The prior art has attempted to produce silicon dioxide or silicon oxynitride or silicon nitride films at temperatures &gt;550.degree. C., at high deposition rates and low hydrogen and carbon contamination. However, the prior art has not been successful in achieving all these goals simultaneously with one silicon precursor. The present invention has overcome the problems of the prior art with the use of a single precursor for the formation of silicon dioxide and silicon oxynitride (as well as silicon nitride), which avoids the problems of plasma deposition, operates at low thermal conditions (&lt;600.degree. C.), avoids Si--C bonds to reduce carbon contamination of the resulting films, has low hydrogen contamination, as well as avoiding chlorine contamination and operates at low pressures (20 mTorr-2 Torr) and up to atmospheric pressures in a manufacturable batch furnace (100 wafers or more) or a single wafer reactor, as will be described in greater detail below.